The 8V71 was first put into buses in 1961 (GM PD4106) The fuel hit was probably worth the extra power. As good an engine as the 6-71 was and even the 6V71, they are both underpowered in some circumstances. Are you still considering the 4905 or have you moved on?

-- Seaton

seaton

I'm still checking the 4905 Went over and started it today I have not found any better yet

This size Parlor used a 4.375:1 rear axle ratio. This works out to about 100 rpm higher at any given road speed than the 35-foot models. Makes sense - the 40-footer's heavier.

Plugging the numbers into the above formula gives you a final drive of 3.535:1 for the stick shift, and 3.806:1 for the V-730.

Real World Mileage -

After 25+ years in the bus industy, IBME that most stick-shift, 8V71-powered 35-foot GMs get 8-9 mpg overall. Some owners, running in the flat mid-west and keeping the speed down to around 60, have reported 10, but that's rare. V-730-equipped models return 1 - 1.5 mpg less.

It really does depend on the routing, winds, weight of right shoe, highway vs city, overall weight of coach, etc.

Because of the limited amount of powertrain options for a V-drive GMC, about the only way to improve mileage (besides parking it and never driving) is to install 24.5" wheels with the tallest 11R24.5 tires you can find. Bridgestone, for example, makes a drive tire that turns 470 revs/mile. This tire will just about bring a V-730-equipped coach back to similar mileage as a stick-shift unit.

The heavier 40-foot MCIs will return 1 - 1.5 mpg less on average than a comparable GMC. Simple physics.

Where a bus really shines compared to a stick 'n staple is in range. A PD4106 with the OEM stick shift powertrain, for example, will go over 1,000 miles on a tank of fuel, and still leave you enough to find a truck stop. So will the 4905, for that matter, but the reserve margin's a little tighter.

Finally, you don't buy a bus for fuel mileage. It's just like the old joke about the Mercedes salesman telling the prospective customer after being asked about a model's fuel consumption: "If you cannot afford the fuel mileage, you cannot afford the car." You buy a bus for the safety and convenience, not mileage.

Mike, I tried the # you left the other day no luck call me at 765 362 3877

andy I'll try on Thurs. If my wife does not get mandated at work. It going to Snow. She is in health care and they can make her stay at work till more people can get in I'll have my 2 kids At 3 & 5 they don't let me talk on the phone

10.00x20s are about 10" wide, 11R22.5 or 24.5 are about 11", and 12R22.5s run about 12" wide, give or take a little.

But wait. . . there's more:

The trucking industry is converting over from the above measurements to metric sizing, similar to your car. 12R22.5s now equal 315/80R22.5 and so forth. You have to go to the charts to find out what metric size equals the old sizing, which is not that difficult, as most manufacturers have that info online. Of course, dealers have it too. . .

The 20" tube-type are becoming more rare, nearly everything's tubeless nowadays. That and many tire shops are refusing to mount split rims like these, primarily for liability reasons.

A GM coach, and it's limited powertrain options, requires you to concentrate on "tire revolutions per mile" when shopping for wheels and tires, as well as load range, speed rating, etc. The magic number is 495. That's the revs/mile GM designed the powertrain around, and the closer you stay to that number, the closer you'll come to OEM performance.

Simple rule of thumb:

Tires that turn MORE than 495 will increase fuel consumption and reduce top speed.

Tires that turn LESS will have the opposite effect.

Be careful shopping for "bus tires." For example, there are two different versions of the common 315/80R22.5 bus tire. One is for transit buses, and one is for highway models. The difference? The transit tires have much heavier sidewalls, to cope with the fact transit drivers think curbs are part of the bus's braking system. They're often limited to 50 or 55 mph, and can easily overheat and self-destruct when subjected to sustained 70 mph speeds. So speed rating as well as load range are two additional concerns when buying tires, in addition to revs/mile.

I got a 72 Flyer D700 6v71 647 auto trans, 4.11 gears 7.5 - 9 mpg U.S towing a jeep driving in British Columbia where it is hard to get over 65 mph with all the hills we have. It's all pretty simple H/P X rpm means fuel consumption. Gerry